Amateur Radio/Scanner & Linux blog

My place in cyberspace for thinking out loud about the Three Rivers Area Montioring Association and its Sunday evening Pittsburgh Area Scanner Net as well as ham radio and the Linux operating system. Feel free to email me with your commenets.

Tuesday, July 25, 2006

A modification for the PRO-83

Here is an interesting tidbit that I picked up from the PRO-83 mailing list on Yahoo. I have a PRO-83 and love the little radio although I have not tried the mod yet. As with any of these types of projects if you are one of those that likes to tinker but is not sure which end of the soldering iron gets hot I advise you to enlist the help of a more experienced friend for this one. Thanks to Eric for his efforts.

This is my first contribution to the group and I hope it helps somefrustrated Pro-83 owners out there. About a year ago I see there wasquite a bit of discussion about the Pro-83 suffering from roaming orrandom birdies in the VHF LO band. My unit fell into that catagory, somuch so it had been nearly impossible for me to listen between30-50Mhz without it stopping on a frequency for a duration of a fewseconds up to 15 minutes before I had to press scan again. I live in arural area and the VHF-LO band is still heavily used by the local firedepartment, and I was damned if I was going to miss out on any of it.

Today I had a few hours to burn and experiment with my Pro-83 and Ihave solved the problem. I'm not an engineer so I can't explain why itworks, I've just used some "old time" techniques from years ago when Ibuilt radio kits as a kid. What you'll need is a small piece of hookupwire, a .0001uf (100pf) mica disc capacitor and basic soldering skills.

1. Remove the back off of the Pro-83 by unscrewing the 6 phillipsscrews, don't forget there's two inside the battery compartment.

2. Carefully separate the front and back and lay face down on acushioned surface or piece of cloth (We don't want to scratch our nicescanners up do we?) Be extra careful not to stress the power leadscoming from the battery compartment to the PCB either.

3. Locate where the antenna BNC connector is soldered to the printedcircuit board. Obviously, it's at the top where the volume and squelchare located. Take note there are 3 solder points on the BNC connector,the one in the middle is the actual connection to the antenna and theother two on the outer most left and right are ground.

4. While looking straight down on the circuit board with the BNC,volume and squelch at the top, solder one end of your hookup wire tothe LEFT ground point of the BNC. Solder the other end of your wire tothe closest corner of one of the tin shields covering the oscillatorsand other components. This should be easy to do since there's plentyof solder blobs on the tin shields already and keep your wire as shortas possible. The idea here is for us to have "positive" contact fromthe antenna ground and the PCB ground bus and we're sure there's noresistance of any kind.

5. Solder one lead from your .0001uf (100pf) capacitor to the centerconnection of the BNC (or antenna connection) where it connects to theprinted circuit board, and the other lead to the RIGHT groundconnection of the BNC, keeping the leads as short as possible on thecapacitor without burning it up with your soldering iron.

Ta-da!, you're done. Carefully slide the front and back togethermaking sure not to pinch or crush the battery leads, replace andtighten the screws and enjoy birdie free VHF-LO scanning.

Now, before you all ask why this works I'll truthfully say I don'tknow. Maybe the engineers can come out of the woodwork. I do know thatnearly every radio kit I built as a kid involved some sort of 100pf or1000pf mica capacitor connected at the antenna as described here toact as a small RF choke...and essentially that's what we want toachieve, choke the RF birdie from getting into the attached portableantenna. As for the hookup wire, there's an added bonus other thenmaking sure our antenna has a "positive" connection to the ground bus.It also appears to improve reception slightly most likely becausethere's no chance of ground resistance and the tin shields now act asa small ground plane.

After making this simple modification I have now been listening to myPro-83 for three hours straight without one birdie lockup on VHF-LOusing a 3 foot telescopic whip. The local fire deparment comes in loudand clear as well as all signals on VHF-HI, UHF and 800Mhz.